In order to cope with the requirements in the communication with a further high-speed and large capacity of mobile communication devices typified by smart phones and tablets, the MIMO technology (Multi-Input Multi-Output) using multiple frequency bands at the same time is beginning to be put into practical use. If the frequency bands used for communication increases, high frequency components are required for each frequency band respectively. Thus, in order to increase the number of the components while maintaining the equipment size, further miniaturization and higher functionality of each component is required.
As such electronic components corresponding to the high frequency, there are components such as a diplexer, a band pass filter or the like. They are all constituted by a combination of dielectric materials functioning as capacitors and magnetic materials functioning as inductors. However, it is required to suppress the losses respectively under a high frequency region in order to obtain a good high frequency property.
Regarding to the dielectric materials, requirements are demanded as follows. (1) Firstly, corresponding to the demand for miniaturization, the relative permittivity (εr) is demanded to be high in order to reduce the area of the capacitor part; (2) secondly, in order to make the selectivity of frequency good, the dielectric loss is required to be small, that is, the Q value is required to be high; and (3) thirdly, the dielectric breakdown voltage is required to be high.
For example, an amorphous SiNx film has a high Q value of about 500 at high frequency (2 GHz) and a dielectric breakdown voltage as high as about 500 V/μm to 700 V/μm, thus, it is generally widely used in the electronic components corresponding to high frequency. However, its relative permittivity is as low as about 7, thus, a large electrode area is required to have a desired function, and it has been difficult to meet the demand for miniaturization. In addition, accompanying with the progress of the communication technology in recent years, a further improvement of characteristics of high frequency components is desired, that is, a dielectric material having a higher Q value and a higher dielectric breakdown voltage is demanded. In order to meet such demands, dielectric films mainly composed of NaCl type alkaline earth metals represented by MgO, CaO or the like have begun to be studied in recent years. As the reason, it is because that a thick film having a thickness of 1 μm or more has characteristics better than the amorphous SiNx film, that is, it has a higher relative permittivity (>7), a higher Q value (>500) and breakdown voltage (>700 V/μm).
In Non-patent Document 1, a technique has been disclosed where a MgO thick film having a NaCl type crystal structure is formed into a thin film having a thickness of less than 1 μm. It is reported that the fabricated MgO thin film has a thickness of 260 nm and a dielectric breakdown voltage (Vbd) of 80 V/μm, while εr=7 and Q=20 under a measuring frequency of 1 KHz.